In a Long Term Evolution (LTE) system, protocol architecture of a user plane at a terminal side includes the following several protocol layers from bottom to top:
a Physical (PHY) layer, which primarily transmits information to a Media Access Control (MAC) layer or a higher layer through a transmission channel;
the MAC layer, which primarily provides data transmission through a logical channel and is responsible for allocation of radio resources to complete functions such as Hybrid Automatic Repeat Quest (HARD), Scheduling (SCH), priority processing, and Multiplexing (MUX) and de-Multiplexing (DEMUX) etc.;
a Radio Link Control (RLC) layer, which primarily provides segment and retransmission services of user and control data; and
a Packet Data Convergence Protocol (PDCP) layer, which primarily completes transfer of user data for Radio Resource Control (RRC) or an upper layer of the user plane.
Under the above protocol architecture, a method for transmitting uplink data by the terminal generally includes:
the terminal establishes Data Radio Bearers (DRBs) with a base station; the base station allocates to the terminal, Logical Channel Groups (LCGs) to which the DRBs belong, herein the LCGs include four subgroups, i.e., 0, 1, 2 and 3 subgroups; when the terminal requires to transmit uplink data and detects that there is no uplink resources or authorization, the terminal transmits a Buffer Status Report (BSR) to the base station, herein the BSR carries an index value corresponding to information about buffer data (i.e., a size of the buffer data) of the radio bearers; herein the size of the buffer data is a sum of sizes of buffer data on the RLC layer and the PDCP layer of the data radio bearers. The base station acquires the size of the buffer data according to the index value in the received BSR, and configures corresponding uplink authorization for the terminal; and after receiving the uplink authorization, the terminal transmits the uplink data. The terminal may report a short BSR or a long BSR or a truncated BSR according to a practical condition.
Due to the short of spectrum resources and the sharp increase of heavy traffic services of mobile users, in order to increase user throughput and enhance mobility performance, a high-frequency point such as 3.5 GHz is used for hotspot coverage, and a node with low power is used. However, the attenuation of signals at the high-frequency point is fast, and a coverage range of a small cell is relatively small and a small cell does not share a site with a related cell. Currently, a lot of companies and operators tend to seek for a new protocol architecture, one of which is Dual Connectivity. Under the Dual Connectivity, the terminal can maintain data connections with more than two service nodes (for example, base stations) at the same time, but the control plane is only connected to one of the service nodes (for example, a base station of a macro cell).
Currently, one of the protocol architectures is to use a manner of split bearer, which is to split a data radio bearer among multiple base stations, i.e., data of one data radio bearer are transmitted through multiple base stations. In this architecture, there is only one PDCP layer of the terminal corresponding to the base station, but various RLC layers correspond to PLC layers on various base stations one by one. Therefore, when the terminal transmits uplink data to the base station, the data on the PDCP layer require to be split and the split data are transmitted to the base stations, and the data on the RLC layers are correspondingly transmitted to corresponding base stations. However, currently, there is no disclosed technical solution about how to report information about buffer data in the BSR based on split bearers. That is, at this time, the base station cannot accurately know the data required to be transmitted by the terminal, and thereby the resources are wasted or are insufficient in the process of the terminal transmitting uplink data.